as I don't know enough info I will say how to figure it out,
so you get the amount of cereal in a [eg 40] then you divide it by 10 you get [4] each cup is worth [4] then you divide b [eg 56] by [4] giving you [14] so you get [4]
more cups of cereal in b.
i am presuming thats the info you get in the question and if it is that is how you answer it if not well its your fault for not providing enough info
